Self-Protection Against Non-Stationary Disturbances

ABSTRACT

Included are embodiments for self protection. At least one embodiment includes Self-protection Unit for protecting a signal that includes a first receiving component configured to receive data, the received data being received as at least one frame and a subframing component configured to subframe at least a portion of the received data, wherein subframing includes converting the at least one into a plurality of subframes. Some embodiments include a subframe interleaver component configured to interleave at least a portion of the subframes.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/754,669, filed Dec. 30, 2005 and U.S. Provisional Application No.60/771,885, filed Feb. 10, 2006, each of which are incorporated byreference in their entireties.

BACKGROUND

In many communications systems, disturbances may be received in aplurality of different forms. More specifically, a communications systemmay receive stationary noise and/or non-stationary noise. Stationarynoise may include Additive White Gaussian Noise (AWGN) and/or othertypes of stationary noise. Non-stationary noise may include impulsenoise and/or other noise that may cause a burst disturbance to areceived signal.

Immunity to both stationary and non-stationary disturbances may beimproved by using a “Signal to Noise Ratio (SNR) margin” (expressed indecibels (dB)), which may be configured to determine the available SNRoverhead in case of a sudden increase in noise variance. Typical marginvalues, which may be in the range of a few dB, may become useless in thepresence of these high-energy bursts. Classical techniques to protectcoded systems against such interferences without the use of externalcodes employ channel interleaving to spread burst-errors, therebyimproving the burst-error-correction capability. However, thesetechniques suffer from one or more technical drawbacks.

Thus, a heretofore unaddressed need exists in the industry to addressthe aforementioned deficiencies and inadequacies.

SUMMARY

Included are embodiments for self protection. At least one embodimentincludes Self-protection Unit for protecting a signal that includes afirst receiving component configured to receive encoded data, thereceived data being received as at least one frame and a subframingcomponent configured to subframe at least a portion of the receiveddata, wherein subframing includes converting the at least one into aplurality of subframes. Some embodiments include a subframe interleavercomponent configured to interleave at least a portion of the subframes.

Also included are embodiments of a method for self-protection. At leastone embodiment of a method includes receiving data, the received encodeddata being received as at least one frame and dividing the at least oneframe into a plurality of subframes, at least one of the pluralityframes being a subset of the at least one frame.

Other systems, methods, features, and advantages of this disclosure willbe or become apparent to one with skill in the art upon examination ofthe following drawings and detailed description. It is intended that allsuch additional systems, methods, features, and advantages be includedwithin this description and be within the scope of the presentdisclosure.

BRIEF DESCRIPTION

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views. While several embodiments are described inconnection with these drawings, there is no intent to limit thedisclosure to the embodiment or embodiments disclosed herein. On thecontrary, the intent is to cover all alternatives, modifications, andequivalents.

FIG. 1 is an exemplary embodiment of noise in a time domain and in afrequency domain.

FIG. 2 is an exemplary embodiment of a self-protection unit, which maybe used to reduce effects of stationary and/or non-stationary noise.

FIG. 3A is an exemplary embodiment of a subframe interleaver, such asmay be utilized in the self-protection from FIG. 2.

FIG. 3B is an exemplary embodiment of a subframe deinterleaver, similarto the subframe interleaver from FIG. 2A.

FIG. 4 is a datagram of a self-protected system with parameters, using asubframe interleaving technique, such as in the self-protection unitfrom FIG. 2.

FIGS. 5A and 5B are exemplary graphical representations of power, suchas Signal to Noise Ratio (SNR) margin, as a function of bit errorprobability for an Orthogonal Frequency Domain Multiplexing (OFDM)system.

FIG. 6 is an exemplary embodiment of a plurality of Bit Error Rate (BER)curves versus power, similar to the diagram from FIGS. 5A and 5B.

FIG. 7 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in protecting a signal from impulse noise, such asmay be utilized in the system from FIG. 2.

FIG. 8 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in providing data to a decoder, similar to theflowchart from FIG. 7.

FIG. 9 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframer, such as the subframer from FIG. 2.

FIG. 10 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a desubframer, such as the desubframer from FIG.2.

FIG. 11 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized for determining subframing strategies, similar tothe flowchart from FIG. 10.

FIG. 12 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframe interleaver, such as the subframeinterleaver from FIG. 2.

FIG. 13 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframe deinterleaver, such as the subframedeinterleaver from FIG. 2.

DETAILED DESCRIPTION

Included are systems and methods for self-protection againstnon-stationary disturbances with a single Parallel ConcatenatedConvolutional (PCC), or Low-Density Parity Check (LDPC) code and/orother codes. Self-protection may include the ability to correct amixture of random-errors and burst-errors to achieve an output Bit ErrorRate (BER) that is below a specified target without using additionalcoding. Such systems may be configured to efficiently utilize anavailable Signal to Noise Ratio (SNR) margin. Additionally included areembodiments of a self-protection unit that that may be configured forerasure-decoding, subframing and subframing interleaving operability.

Systems using a multicarrier modulation scheme, such as OrthogonalFrequency Division Multiplexing (OFDM) and Discrete MultiTone (DMT)modulation schemes, may be sensitive to burst noise since a burstcorrupting a few time-domain samples may spread across subcarriers of acorresponding multicarrier symbol after a conversion from time-domain tofrequency domain.

As a nonlimiting example, for a system using an OFDM or DMT modulation,a burst signal that corrupts one or more time-domain samples may spreadacross subcarriers of a corresponding OFDM and/or DMT symbol when a FastFourier Transform (FFT) operation is performed at a receiver. Hence, theburst length after an FFT operation may equal an integer multiple of thesymbol length (see for example, FIG. 1).

Additionally, burst errors may be associated with an energy level thatis significantly higher than the SNR margin. Consequently, the entiresymbol affected by a burst may be severely corrupted. Such symbols carryvery little information to help a decoder, and may be erased.

Assuming perfect synchronization and equalization, the equivalentfrequency-domain channel model that jointly accommodates random- andburst-errors may be represented by a memory-less channel disturbed bytwo noise sources: 1) a stationary background Additive White GaussianNoise (AWGN), and 2) non-stationary Symbol-Erasures (SE) correspondingto frequency-domain bursts, called error events. For each symbol k, thechannel input maybe represented by a vector x_(k) where each elementcorresponds to the constellation signal transmitted per subcarrier. Thechannel output is then a vector y_(k) as defined in expression (1):

$\begin{matrix}{y_{k} = \left\{ \begin{matrix}* & {{if}\mspace{14mu} {symbol}\mspace{14mu} k\mspace{14mu} {is}\mspace{14mu} {corrupted}} \\{{a\; \; x_{k}} + n_{k}} & {{otherwise},}\end{matrix} \right.} & (1)\end{matrix}$

where

stands for the element-by-element vector product, the vector a denotesthe attenuation per subcarrier, n_(k) is a white Gaussian noise vectorwith zero mean and variance σ², and * represents a symbol-erasure.

More specifically, in at least one exemplary embodiment, the channelcoding process is assumed to be such that a codeword (often referred toas a frame) may be composed of an integer number η of symbols. Based onthe channel model, a WC-AWGN-SE channel may be introduced to evaluatethe ability of a coded multicarrier system to correct isolatedworst-case error events corrupting “α” consecutive symbols. An isolatedworst-case error event may include scenario where an arrival timebetween two error events is sufficiently large so that no more than oneerror event affects a single frame. Thus, a WC-AWGN-SE (η, α, σ²)channel may be configured to assume that each frame comprised of ηsymbols has a (integer) contiguous symbol-erasures. Since α may be aninteger, a frame can be corrupted by a limited number η−α+1 of distinctlength-α error events uniformly located in the length-η frame. Thelocation of symbol-erasures is assumed to be known by the decoder, whichis practically valid for OFDM systems. The ratio P_(f)=α/η is defined asthe frame erasure rate (FER).

As a nonlimiting example, a fully coded OFDM system may be configured totransmit data over a WC-AWGN-SE (η, α, σ²) channel. Assuming that thelocation of symbol erasures is available at the decoder, some techniquesto improve the system performance without additional coding combineerasure decoding and channel interleaving whose functions are distinct.

Erasure-decoding may include setting to zero the log-likelihood metrics(sent to the decoder) of bits associated with symbol-erasures. Given thedesign decoder output BER P_(b) in a pure AWGN(σ²) environment, it isusually (but not always) possible to maintain P_(b) in a WC-AWGN-SE (η,α, σ²) environment by increasing the signal power by the amount Γ(P_(f),P_(b)). Given the uniform occurrence probability of error events in aWC-AWGN-SE environment, Γ(P_(f), P_(b)) is obtained by averaging the SNRdegradation (relative to the AWGN performance) due to simultaneouslyerasing the α N/η contiguous bits with indices (ζ−1)N/η+1 to (ζ+α−1)N/ηin the N-bit frame, for all starting locations ζε {1, . . . ,η−α+1} oferror events. Therefore, a configuration with an SNR margin Γ_(s) canachieve a decoder output BER of P_(b) in a WC-AWGN-SE (η, α, σ²)environment as long as P_(f)<P_(f,max,) where P_(f,max,) is the maximumvalue P_(f) yielding Γ(P_(f),P_(b))≦Γ_(s).

If P_(f)>P_(f,max,) erasure-decoding is insufficient to ensure a BER ofP_(b) with the SNR margin. In this case, channel interleaving may beused, which involves reordering the bits of each original frame into aninteger number D≧1 of frames in order to reduce the number of contiguouscorrupted bits per frame. Hence, if an error event affects a frame inthe channel, the error may actually corrupt non-contiguous bits spreadacross D different original frames, in which the number of erasures maybe reduced by a factor of approximately D. For D=1. Although theoriginal FER P_(f) remains unchanged, the effect of interleaving thebits in a frame may reduce Γ(P_(f),P_(b)), thereby increasingP_(f,max,). D is called the interleaving depth. Two classes of channelinterleavers may be used in communications systems: random channelinterleaver and convolutional channel interleaver.

A random channel interleaver (RCI) may be configured to randomlyinterleave the coded sequence in order to spread and randomize corruptedbits into D frames. Since PCC and LDPC codes may be designed toeffectively correct random-errors, random interleaving represents a goodsolution to improve the erasure correction capability per frameP_(f,max,) (e.g., to lower Γ(P_(f),P_(b))). However, given its blockstructure, the RCI may introduce an extra latency equal to twice thedelay of transmitting D−1 frames and also requires the interleavingpattern to be stored.

A Convolutional Channel Interleaver (CCI) is a synchronous interleaverthat cyclically spreads error events. The CCI is particularlyadvantageous in applications that only demand improved spreadingcapabilities, since the CCI can achieve the minimum possible latency(half that of the RCI) with a minimum storage capacity. The CCI does notrequire storage for an interleaving pattern. However, given its periodicdeterministic interleaving pattern, the CCI does not randomize thelocation of corrupted bits, hence does not guarantee an erasure-decodingperformance as good as that obtained with the combination oferasure-decoding and RCI of similar depth.

Self-protected systems may be configured for erasure-decoding with anenhanced channel interleaver that combines the high erasure correctioncapability of the RCI with the low latency and storage capacity of theCCI. A new channel interleaver may be formed by the serial concatenationof a subframer 204 and a subframe interleaver 206, whose operations aredetailed below.

Referring now to the drawings, FIG. 1 is an exemplary embodiment ofnoise in a time domain and in a frequency domain. More specifically, asillustrated in the nonlimiting example of FIG. 1, in receiving amulti-carrier signal, noise 102 a, 102 b, and 102 c may be received inthe time domain. As illustrated, noise signal 102 a may span a pluralityof symbols. Noise signals 102 b and 102 c may each span only a portionof a symbol. However, when the signal is transformed from the timedomain to the frequency domain, the noise is also transformed. Asillustrated, noise 102 a is transformed into a frequency-domain impulsevector 104 a that spans two full symbols. The noise signal 102 b istransformed into a frequency-domain impulse noise vector 104 b thatspans a full symbol. The noise signal 102 c is transformed into afrequency-domain impulse noise vector 104 c that also spans a fullsymbol. As transforming the signal from the time domain to the frequencydomain also transforms noise on that signal, a Self-Protection Unit(SPU) may be utilized to reduce the effects of the noise.

FIG. 2 is an exemplary embodiment of a self-protection unit, which maybe used to reduce stationary and/or non-stationary noise. Morespecifically, as illustrated, an encoder 202 may receive data bits forprocessing. The encoder may encode the received data and send theencoded data to a subframer 204 of the Self-Protection Unit (SPU) 200.The subframer may receive the encoded data as code words in frames,where each frame may include a plurality of bits (and/or bytes), suchas, for example 255 bytes. The subframer may be configured to divide thereceived frames into a plurality of sub-frames, where one or more of thesubframes may be configured as a subset of a received frame.

Subframing may include reordering the elements of a single frame inorder to reduce the SNR degradation Γ(P_(f),P_(b)), thereby increasingP_(f,max,). Depending on the particular configuration, subframing may becompleted in two steps. First, the subframer 204 may determine a set ofN/η-bit subsets F₁, i ε {1, . . . ,η} of the frame F, such thatF_(i)∩F_(j)=Ø,∀{i,j≠i} ε {1, . . . ,η}² and

$F = {\overset{\eta}{\bigcup\limits_{i = 1}}F_{i}}$

such that the average SNR degradation due to simultaneously erasing allbits of the sets

${\overset{\zeta + \alpha - 1}{\bigcup\limits_{i = \zeta}}F_{i}},$

is reduced (compared to erasing αN/η contiguous bits in the frame.

Second, the original frames may be reordered so that all bits in F_(i)are contiguous in the reordered frame, which comprises η contiguousblocks, called subframes, respectively containing the bits in thesubsets F₁ to Fη. The reordering of the original frame into subframes isdictated by a so-called subframing pattern, noted S_(η) ^(α.)

Subframing does not modify the system latency, which may be configuredto equal (or substantially equal) the delay to encode and decode a frame(2η symbol times). However, both transmitter and receiver may beutilized to store the subframing pattern and the reordered frame. Thechoice of subsets F_(i)'s to maximize P_(f,max,) depends on thestructure of the code. Various embodiments of this disclosure may beconfigured to provide a memory efficient approach to determine a set ofF_(i)'s that both increases P_(f,max,) and yields a cyclic subframingpattern of small period, hence utilizing small storage capacity.

By increasing P_(f,max,) subframing can maintain P_(b) with a higher FERP_(f) without interleaving several frames together. If P_(f)≦P_(f,max,)each subframe may be mapped to a symbol transmitted over the WC-AWGN-SEchannel. However, in the case P_(f)>P_(f,max,) subframing may beinsufficient and the use of additional techniques, such a subframeinterleaving, may be utilized.

A subframe interleaver 206 may also be included in the Self-ProtectionUnit 200 and may be configured to receive the subframes from thesubframer 204. The subframe interleaver 206 may also be configured tointerleave the received subframes to reduce the effect of impulse noiseon a signal. More specifically, as discussed in more detail below, asimpulse noise may span the length of one or more subframes. In order toreduce the number of subframes associated with any given frame that areaffected by received impulse noise, at least one embodiment may beconfigured to interleave and/or otherwise rearrange the subframes. Insuch a configuration, received impulse noise may span the length of aplurality of subframes, however, since the subframes are interleaved,only a fraction of the subframes associated with a given frame areaffected. This may enhance the performance of a decoder 222 and/or othercomponents illustrated in FIG. 2.

The interleaved subframes may be sent from the subframe interleaver 206of the Self-Protection Unit to a constellation mapper 210. Theconstellation mapper 210 may be configured to map bits of the subframesto the same OFDM symbol, as discussed in more detail, below. The mappeddata may then be sent to a transmission channel 212. The transmissionchannel 212 can be configured to evaluate the performance of the system.One should note that transmission channel 212 can be a wireless channel,wireline channel, and/or other channel for evaluating the performance ofthe system.

Additionally the transmission channel 212 may send the data to aconstellation demapper 214 for demapping the data. The demapped data issent to a subframe deinterleaver 218, which may be configured todeinterleave the received data. Additionally, a symbol error detector216 may be included and configured to flag a confidence signalassociated with the accuracy of the received data. Upon deinterleaving,the data may be sent to a desubframer 220 to return the subframes backto a frame format. The data may then be sent to a decoder 222.Additionally, an off-line calibration component 208 may be configured toreceive a code type and (among other things) determine a distance intime between subframes.

FIG. 3A is an exemplary embodiment of a subframe interleaver, such asmay be utilized in the self-protection from FIG. 2. As illustrated, thesubframe interleaver 206 can receive a plurality of sequential subframesat input 320.

More specifically, in at least one nonlimiting example, subframeinterleaving may be introduced to spread isolated error events overseveral subframes associated with distinct original frames, therebyreducing the original FER P_(f). The subframe interleaver 206 may beconfigured to operate on subframes and may be used for a spreadingcapability via a convolutional structure. Any of a plurality of subframeinterleaving techniques may be utilized, a plurality of which arediscussed below.

A first interleaving technique, inspired by Forney's approach, mayinvolve 1) reordering according to the subframing pattern S_(Dη) ⁶⁰ eachframe in Dη subframes, where D=┌α/ηP_(f,max)┐, and 2) interleavingsubframes so that each symbol includes at most a single subframe from aspecific frame. The original FER P_(f) (=α/η) may then be reduced by afactor D. This technique may be configured to introduce a minimum extralatency of

$\left( {\left\lceil \frac{\alpha}{\eta \; P_{f,\max}} \right\rceil - 1} \right)\eta$

symbol times.

In a second Interleaving technique, each original frame may be reorderedinto Dη subframes according to S_(Dη) ¹, where D=┌1/ηP_(f,max)┐. Thesubframes are then interleaved so that no contiguous sequence of asymbols contains more than one subframe taken from the same originalframe. A convolutional interleaver may be utilized and configured torealize such interleaving and introduce an extra latency equal to (insymbol times)

${{\left( {{\left\lceil \frac{\alpha}{\eta \; P_{f,\max}} \right\rceil \eta} - 1} \right)\alpha} - \eta + \left( {\eta,\alpha} \right)},$

where (η,α) denotes the greatest common divisor of η and α.

Given the parameters {η,α,P_(f,max)}, in various embodiments, one mayselect the technique (first or second, described above) that yields thelowest latency. Thus, subframe interleaving introduces at most an extralatency equal to that of the classical CCI. When the equations aboveproduce equal (or substantially equal) results, the second technique maybe selected since this algorithm interleaves fewer subframes, thusrequiring less memory and less latency. In many embodiments, Dη<<N,hence the storage capacity of the subframe interleaver 206 (Dη subframeindices) may be almost negligible compared to that of a bit-CCI (Nbits). The bits in each subframe may be stored in the subframer 204.

By using subframe interleaving of depth D, a length-α error eventcorrupts at most D if the first technique is utilized (or α D if thesecond technique is utilized) different original frames if theinterleaving techniques described above are used. Therefore, to becapable of maintaining the target BER of P_(b) for D≠1, the transmissionchannel 212 may be configured to assume Dη (first technique) and αDη(second technique) symbols per frame (e.g., an increased arrival timebetween error events) depending on which interleaving technique is used.

FIG. 3B is an exemplary embodiment of a subframe deinterleaver, similarto the subframe interleaver from FIG. 2A. More specifically, asillustrated in the nonlimiting example of FIG. 3B and discussed in moredetail below, the subframe deinterleaver may be configured to receive aplurality of subframes from the erasure component 217 and deinterleavethe received subframes according to the previously determined strategy.The subframe deinterleaver may output deinterleaved subframes todesubframer 220 via output 322.

FIG. 4 is a datagram of a self-protected system with parameters, using asubframe interleaving technique, such as in the self-protection unitfrom FIG. 2. More specifically, with respect to the Off-line calibration208, given the code (type, η), the SNR margin Γ_(s) and the target BERP_(b), one may first determine P_(f,max,). If P_(f)≦P_(f,max,) set D=1,select S_(η) ^(α) from a table (that stores the patterns S_(η) ^(α) forvarious combinations {η,α}) and bypass the subframe interleaver.Otherwise, one may select the subframe interleaving technique yieldingthe lowest latency, compute D, and then select S_(Dη) ⁶⁰ (firstinterleaving technique) or S_(Dη) ¹) (second interleaving technique)from a table.

During a transmission mode after encoding, each frame may be reorderedaccording to S_(Dη) ^(α) (first interleaving technique) or S_(Dη) ¹(second interleaving technique) into Dη subframes with labels in {1, . .. ,Dη}. The subframes may then be interleaved using the selectedtechnique (first or second). Finally, the D interleaved subframesforming each symbol k may be mapped (via constellation mapper 210 (FIG.2) to a vector x_(k) transmitted over the channel 212 (FIG. 2). At areceiver of the SPU 200, if the received vector is corrupted (y_(k)=*)(represented by the hatched area in FIG. 4), all metrics associated withthe symbol k may be erased via eraser 217, otherwise the metrics arecomputed assuming a pure AWGN with zero mean and variance σ². Finally,subframes may be deinterleaved, via subframe deinterleaver, 218 (FIG. 2)and desubframed, via desubframer 220 (FIG. 2) into the originalbit-ordering, before decoding.

As codes designed to correct random errors are also likely to performwell in the presence of random erasures, a reasonable model to tacklechannel erasures might involve randomly distributing the erasuresthroughout the frame. Thoroughly, the concept of random erasures canserve as a basis for a reference subframing strategy, which may includerandom subframing. Random subframing may include randomly reordering theoriginal coded bit sequence into η complementary subframes. Althoughrandom subframing yields fairly good performance for both PCC and LDPCcodes, the technique may require storing the N-bit subframing pattern.Thus, various embodiments may be configured to provide deterministicsubframing strategies for PCC and LDPC codes that are nearly aseffective in performance as random subframing in terms of P_(f,max,) butthat reduce the storage capacity for the subframing pattern.

At least one exemplary embodiment may utilize a rate-R PCC Code (R≧⅓)obtained by puncturing a rate-⅓ PCC code. When using an iterative aposteriori probability decoder, the systematic, non-interleaved parity,and interleaved parity bits (respectively denotes as s_(n), p_(n)n ε{1,. . . ,N}) may have different levels of importance. Given the highimportance of systematic bits and the regular trellis structure, oneexemplary embodiment involves cyclically puncturing only the two paritysequences so that punctured elements are: 1) alternately and equallydistributed in both sequences, and 2) well scattered in each sequence.

Puncturing bits at the transmitter yields similar performance to erasingthe same bits at the receiver. Consequently, a system using subframingdictated by S_(η) ^(α) is equivalent to a system punctured by α constantpuncturing patterns (CCP's) uniformly selected from a set of η CPP'sthat respectively puncture all bits contained in each subset F_(i),following by transmitting over an AWGN (σ²) channel. Thus, a good set ofF_(i)'s is given by a set of CPP's jointly optimized to lower the SNRdegradation in an AWGN environment. The joint determination of CPP's isslightly different from the puncturing strategy stated in the previousparagraph. By extending this strategy to the three sequences, a goodsubframing technique (referred to herein as “strategy 2”) may beprovided by first, alternately and equally distributing systematic,parity, and interleaved parity bits to subframes. Next, the coded bitsgenerated by the same data bit may be distributed into differentsubframes. Third, for each coded sequence, all bits allocated to thesame subframe may be scattered in the original ordering. Fourth, thesubframes are complementary.

At least one cyclic subframing pattern with a small period that is aseffective as random patterns can be constructed using the strategy 2.The same cyclic pattern S_(η) ^(α) can be used for any α. However, the ηsubframe indices should be permuted to minimize the average SNRdegradation due to uniformly erasing α subframes with contiguousindices.

As a nonlimiting example, the rate-R=½ PCC code may be configured togenerate an originally ordered coded sequence (s₁, p₁, s₂, p₂, s₃, p₃, .. . ). For η=4, a good 16-periodic subframing pattern determined via thesecond strategy is given by S₄ ^(α)=[1234214213312443]. The subframercan be realized with a η-position commutator distributing the η^(th)coded bit, η ε{1, . . . ,N} to the subframe with index S₄ ^(α (η%) 16),where % denotes the modulo operator.

Thus far, two different subframe interleaving techniques have beensuggested without proving the existence of interleaver devices thatachieve desired latencies. Below is a discussion of a convolutionalsubframe interleaver that achieves the desired latencies with a reduced(even minimum, in some cases) storage capacity. The generic structuresof the subframe interleaver 206 and deinterleaver 218 are depicted inFIG. 2. The interleaver 206 is formed by the serial concatenation of twointerleaver devices. The symbol interleaver, is inspired by Ramsey'stype I/III interleavers and may be configured to interleave thesubframer 204 output symbols (whose length may be equal to that of anOFDM symbol), where a symbol may include a multicarrier symbol. Thesecond device is a periodic interleaver that interleaves the subframesassociated with each output symbol of the first interleaver. For thesake of storage, both devices interleave the subframe indices assumingthat the data contained in each subframe is contiguously stored inmemory.

The interleaver parameters differ with respect to the selectedinterleaving technique (first or second). The first Interleavingtechnique is simpler to implement and can be realized with a singleperiodic interleaver device. Consequently, as discussed below, bothinterleaver devices forming the subframe interleaver are detailed whileassuming that the second interleaving technique is selected. Thepossibility of interleaving according to the first technique with thestructure given in FIG. 2 is discussed below.

The interleaver may be formed by a serial concatenation of twointerleaver devices. The first device, called a symbol interleaver, isinspired by Ramsey's type I/III interleavers and interleaves thesubframer output symbols. The second device is a periodic interleaverthat interleaves the subframes associated with each output symbol of thefirst interleaver.

The symbol interleaver is formed by a Δ₁-stage shift register and aη-position commutator that are both clocked every OFDM symbol time. Eachstage of the shift register stores the D subframe indices associatedwith each symbol output of the subframer. The total number of stages isgiven by Δ₁=(Dη−1)α−η+(η,α)−(D−1)B, where

$B = {\frac{\alpha\eta}{\left( {\eta,\alpha} \right)}.}$

Given the label i ε {1, . . . , η} of a symbol in each frame (i=1+(k−1)%η), the i^(th) symbol is delayed by σ_(i) symbols, where σ_(i) is givenby the recursive formula

σ₁=0

$\sigma_{i} = {\sigma_{i - 1} + \left\{ \begin{matrix}{\alpha - 1} & {{\forall{i > 1}},{\left\lfloor \frac{i - 1}{\left( {\eta,\alpha} \right)} \right\rfloor = \left\lfloor \frac{i - 2}{\left( {\eta,\alpha} \right)} \right\rfloor}} \\{\alpha + {\left( {D - 1} \right)B}} & {otherwise}\end{matrix} \right.}$

The shift register has η outputs, labeled i, which respectivelycorresponds to the outputs of the σ_(i) ^(th) register stages and areη-periodically sampled by the commutator. Unlike Ramsey's structure, theoutputs are not evenly distributed in the shift register, which yields amore complex commutation sequence, that is: the i^(th) output is sampledwhen the shift register inputs the symbol with label 1+(i+σ_(i)−1)% η,for all i ε {1, . . . , η}.

As discussed above, the symbol (first device) deinterleaver is inspiredby Ramsey's type II/IV unscramblers and is formed by a shift registerand a commutator similar to those used in the symbol interleaver, wherethe commutation is performed in the same order as in the interleaver206.

As illustrated, the first device interleaving-deinterleaving latency maybe configured to equal the maximum delay introduced by the interleaver206, (e.g., equals Δ₁). Similar to type I-to-IV interleavers, since eachshift register stores Δ₁ symbols, the combined storage capacity of bothsymbol interleaver and deinterleaver devices 2 Δ₁ symbols, whichcorresponds to twice the minimum possible storage capacity. Although astorage-reducing technique (minimizing the storage capacity to Δ₁symbols) similar to that proposed by Ramsey in J. L. Ramsey,“Realization of optimum interleavers,” IEEE Trans. Inform. Theory, vol.16, no. 3, pp. 338-345, May 1970, which is hereby incorporated byreference in its entirety, is applicable to the symbol interleaver, thestorage reduction is not discussed in this paper for brevity. The symbolinterleaver, in this particular nonlimiting example, has no restrictionson the values of η, D and α.

Once a symbol is interleaved, the D constituent subframes may beinterleaved by a BD×D periodic subframe (second device) interleaver. Theperiodic subframe interleaver may be formed by a bank of D paralleldelayed lines, where the j^(th) subframe, j ε{1, . . . , D} delays thej^(th) subframe constituting each input symbol (through a (j−1)B-stageshift register clocked every symbol. At each symbol time k, the Ddelayed lines output the D subframe-indices associated with thetransmitted symbol x_(k). The associate periodic deinterleaver may havea structure similar to that of the interleaver, except that the delay ofthe j^(th) line equals (D−j)B symbol times. The latency of the periodicinterleaver-deinterleaver, noted Δ₂, equals (D−1)B symbol times. Thestorage capacity of the periodic interleaver (and deinterleaver) may beminimum.

Assuming that the second interleaving technique is selected, the latencyΔ of the subframe interleaver-deinterleaver depicted in FIG. 2 equalsΔ₁+Δ₂=(Dη−1)α−η+(η,α) symbol times. A lower bound on theinterleaving-deinterleaving delay, noted Δ_(min) (expressed in symboltimes), may be achieved when a contiguous sequence of α symbols in theinterleaved sequence contains subframes associated with α D contiguousframes, yielding Δ_(min)=(Dη−1)α−η+1. One should note that Δ_(min)assumes no overlap between interleaved subframes, thus, this may not beachievable for all sets {η,D,α}. At the very least, however, Δ may be aminimum when η and α are relatively prime, since Δ_(min) is achieved.

Assuming that the first interleaving technique is selected, the subframeinterleaver given in FIG. 2 can be simplified to the single periodicsubframe interleaver (in at least one exemplary embodiment, seconddevice only, no first device symbol interleaver is required) with B=η,by setting B=η and forcing the commutator of the symbol interleaver tosample the register output 1 for all i, thereby passing the symbolinterleaver. Since Δ₁=0, the subframe interleaving latency is given byΔ=Δ₂=(D−1)η.

A goal of the various embodiments of this disclosure is to present goodmemory-efficient subframing strategies that can be generally applied toany PCC or LDPC code. For both PCC and LDPC codes, such optimization maydepend on the code structure and would involve joint consideration ofthe subframing pattern with the code structure. For instance, forsystems using PCC codes, the subframing pattern can be optimized tomaximize the minimum output weight and/or minimize the multiplicity oflow weight codewords of the equivalent punctured system.

FIGS. 5A and 5B present simulation results for two different OFDMsystems transmitting QPSK signals per subcarrier over a WC-AWGN-SE(η,α,σ²) channel, which are respectively coded with a rate-R=½ and ⅘ PCCcode. Each PCC encoder is formed by the parallel concatenation of two(23, 35)₈ recursive systematic convolutional encoders separated by arandom interleaver of size 2000 (or 3200) bits for R=½ (or ⅘). Hence,both codes generate 4000-bit codewords. Bit-by-bit Log-MAP decoding with8 iterations is performed. Note that simulations for both Strategies 1and 2 yielded similar performance (within 0.1 dB). Due to the negligibledifference in performance, FIGS. 5A and 5B show the relationship betweenΓ and {P_(f),P_(b)} for the random subframing only, as it is easier tosimulate (although more memory intensive to implement).

Another embodiment provides a subframing strategy for LDPC codes thatrequires no additional storage. The simplest subframing strategy,labeled as Strategy 3, involves allocating sets of N/η contiguous bitsin the frame to distinct subframes. Monte Carlo simulations for arandomly-constructed regular rate-R=½ systematic LDPC code of lengthN=4000 bits on the WC-AWGN-SE channel with sum-product decoding haveshown that the average BER performance based on erasing each possiblecombination of α contiguous subframes obtained via Strategy 3 is almostindistinguishable from the BER performance obtained via randomsubframing. The similarity in performance for random subframing andstrategy 3 is most likely due to the fact that the parity-check matriximplicitly provides a form of random interleaving by introducingdependencies between bits that are scattered throughout the codeword.Explicitly providing a random interleaver, as done in random subframing,thus is superfluous. Note that applying Strategy 3 to PCC codes resultsin worse performance as compared to random subframing due to the factthat the systematic and parity bits associated with the same data bitare simultaneously erased, which results in poor decoding performance.

For both PCC and LDPC codes, we observed that FER values P_(f)>1−R aswell as values of P_(f)<1−R, but near 1−R may not be corrected. As anonlimiting example, for the considered rate —R=½ LDPC code, P_(f)=⅜resulted in an asymptotic BER (BER obtained on the WC-AWGN-SE when σ²→0)of 10⁻² with random subframing. This clearly indicates the existence ofa cutoff value for the FER that can be corrected with asymptoticallyvanishing BER for a given LDPC code. If the FER is above the cutoffvalue, the lowest achievable BER is limited by a hard error floor. FIGS.5A, 5B also shows Γ obtained with random subframing for the (4000, 2001)LDPC code and the (4095, 3367) Euclidean geometry LDPC code.

In practice, Γ(p/q, P_(b)) is simulated with a deterministic subframingpattern S_(q) ^(p) (determined with strategy 2 or 3) for various sets ofintegers {p, q}. Then, Γ(p/q, P_(b)) and S_(q) ^(p) are stored in atable (ROM) used in the SPU calibration to determine P_(f,max). For eachinput {p, q, P_(b)}, the table outputs Γ(p/q, P_(b)) and S_(q) ^(p). Bydefinition P_(f,max) is the highest correctable FER with Γ_(s). However,practically, P_(f,max) may be set as the maximum value of p/q (in thetable) yielding Γ(p/q, P_(b))<Γ_(s). For example, given the limited setof simulated curves presented in FIG. 5, a system with {Γ_(s), P_(b)}={6dB, 10⁻⁵} that uses the LDPC (4000,2001) code has P_(f,max)=⅓.Similarly, a system with identical {Γ_(s), P_(b)} but using thePCC(4000, 2000) code has P_(f,max)=⅜. The precision of P_(f,max)obviously depends on the number of different FER's that have beensimulated.

FIG. 6 is an exemplary embodiment of a plurality of Bit Error Rate (BER)curves versus power, similar to the diagram from FIGS. 5A and 5B. Thecurve (a) of FIG. 6 represents the error performance over an AWGNchannel of a rate R=½ turbo coded OFDM modulation scheme transmitting 4coded bits per tone, where each tone is mapped to a 16-QAM signal setusing Gray labeling. The turbocode is formed by the parallelconcatenation of two 16-state recursive systematic convolutional encoderwith generator polynomials (31, 27)₈ separated by a pseudo-randominterleaver of length of 2052 bits.

For this specific example, we evaluated with Monte-Carlo simulations theperformance degradation due to deleting (setting to zero) the metricsassociated with a single corrupted symbol per turbo frame. For eachsimulated turbo frame, the location of the corrupted (i.e., deleted)symbol is chosen randomly with a uniform probability.

Following strategy 2, the curves (b) and (c) of FIG. 6 illustrate theBER performance degradation for P_(f) =⅓ and ¼, respectively. ForP_(f)=⅓, a SNR gap of 5.5 dB between (a) and (b) is observed at 10⁻⁷BER. Stated differently, assuming a SNR margin larger than 5.5 dB, it ispossible to correct the turbo coded information with a BER lower than10⁻⁷ if less than ⅓ of the turbo frame is corrupted by impulsive noise.For P_(f)=¼, the margin is reduced to about 3 dB.

The capability of correcting impulse events may depend on both the codecharacteristics and margin. The nonlimiting example above shows that fora specific code with rate R=½, the information can be corrected with 5.5dB margin for turbo frames with less than ⅓ of the bits in a turbo frameare corrupted by impulsive noise. For the same code, the margin requiredto correct a corrupted symbol for P_(f)=½ becomes 13.5 dB. For P_(f)=1,since all the bits are corrupted, the code generally does not offer anyprotection against impulse noise.

Based on the observation that highly punctured turbo codes can maintaina target QoS (Quality of Service) with a few dB SNR margin, aself-protection method has been presented to protect TTCM-codedOFDM-based systems against non-stationary noise. Compared to classicalsystems, protecting all the data with a RS code, self-protected systemsmay have a reduced latency. As a nonlimiting example, a self-protectionmethod may be used to reduce the latency of TTCM-coded VDSL-DMT systemswhile maintaining the standard INP requirements.

Various embodiments disclosed herein may be configured to provideefficient combinations of erasure-decoding and channel interleaving,called “self-protection” to correct a mixture of AWGN andburst-erasures, where the available SNR margin is used to reduce thetransmission delay. Self-protection as discussed herein may involveincreasing erasure correction capabilities per codeword by usingsubframing and, if necessary, reducing the number of erasures percodeword by interleaving several codewords together. Variousmemory-efficient subframing strategies for PCC and LDPC codes may beused that require reduced storage resources as compared to randomsubframing. More specifically, some embodiments of subframing strategiesmay be configured to provide similar performance to random subframing.Also, a realization of an interleaver device 206 is provided and may beconfigured to interleave large blocks of bits (called subframes) and mayachieve, with a reduced storage capacity, and a latency at most equal tothat of the classical convolutional channel interleavers. Simulationresults demonstrate that the SNR margin required for maintaining a givenquality of service (target BER and frame erasure rate) may besignificantly lower for PCC codes compared to LDPC codes. Consequently,PCC codes may be utilized in self-protected OFDM systems.

FIG. 7 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in protecting a signal from impulse noise, such asmay be utilized in the system from FIG. 2. More specifically, asillustrated in the nonlimiting example of FIG. 7, an SPU 200 can receiveencoded data (block 732). The encoded data may be received from anencoder that is external from the SPU 200, however this is not arequirement. The SPU can then subframe at least a portion of thereceived data (block 734). More specifically, as discussed above, theSPU may include a subframer, which may be embodied in hardware,software, and/or firmware. The subframer may be configured to convertthe received data, which may arrive as a plurality of frames, intosubframes. The SPU 200 can then interleave at least a portion of thesubframes (block 736). As discussed above, interleaving may take any ofa plurality of different forms, but is generally performed at thesubframe level. The SPU 200 can also send at least a portion of thesubframed, interleaved data to a mapper (e.g., constellation mapper210), as illustrated in block 938.

FIG. 8 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in providing data to a decoder, similar to theflowchart from FIG. 7. As illustrated in the nonlimiting example of FIG.8, the SPU 200 receives data from the channel 212 (block 830). The SPU200 can then determine whether a received symbol is corrupted bynon-stationary noise (block 832). As discussed above, data may be sentfrom the SPU 200 to a constellation mapper 210. The constellation mappercan map the data, as discussed above and send the mapped data to achannel 212, which can send the data to a constellation demapper 214,which can demap the data to be sent back to the SPU 200. The SPU canthen determine via the symbol error detector 216 whether the receivedsymbol is corrupted or not by non-stationary interference (block 834).If the symbol is corrupted (block 833), the SPU 200 can send zeros(block 835). If, at block 833, the symbol is not corrupted, the SPU 200can send a demapped receive symbol (block 834). More specifically, asdiscussed above, the symbol error detector 216 can determine thelocation of a corrupted symbol and flags the symbol with a 0 (if notcorrupted) or a 1 (if corrupted). If the symbol is corrupted, thesubframe deinterleaver 218 inputs zeros instead of the received datafrom the demapper 214. Otherwise, the SPU 200 can deinterleave thereceived data from the demapper 214 via, for example, the subframedeinterleaver 218 (block 836). The SPU can desubframe the received data,via the desubframer (block 838). The SPU 200 can send the desubframeddata to the decoder 222 (block 840).

FIG. 9 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframer, such as the subframer from FIG. 2.As illustrated in the nonlimiting example of FIG. 9, the SPU 200 canreceive an N-bit frame F from the encoder 202 (block 932). Uponreceiving the frame, the SPU 200 can divide the frame into Dη subframes.More specifically, i can be set to 1 (block 934). The subframer 204 canthen select the i^(th) bit of the frame and store this bit contiguouslyin the subframe F_(j) (FIFO memory) where j=S(i) (block 936). Morespecifically, S may be a subframing pattern obtained from an offlinecalibration. j may be a value in {1, 2, . . . , Dη}.

A determination can be made whether i equals N (block 938). If i doesnot equal N, the subframer can set i=i+1 (block 940) and the flowchartreturns to block 936. If i equals N, the subframes F₁, F₂, . . . ,F_(Dη) (and/or addresses associated with these subframes) can becontiguously sent to the subframe interleaver 206.

FIG. 10 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a desubframer, such as the desubframer from FIG.2. As illustrated in the nonlimiting example of FIG. 10, the SPU cancontiguously receive Dη subframes F₁, F₂, . . . F_(Dη) (and/or memoryaddresses associated with these subframes) from the subframe interleaver206 (block 1032). The desubframer 220 can then merge Dη subframes into aframe. More specifically, in at least one nonlimiting example, thedesubframer 220 can set i equal to 1 and point to the first address ofthe subframes (FIFO memories) F₁, F₂, . . . F_(Dη) (block 1034). Thedesubframer 220 can select j, such that j=s(i) (block 1036). Morespecifically, in at least one embodiment, s may be a subframing patternobtained from the offline calibration component 208. j may be a valueselected from {1, 2, . . . , Dη}. The desubframer 220 can then selectthe bit pointed in the subframe F_(j) and store that bit in the i^(th)bit position of the frame F (block 1038). The desubframer 220 can thenpoint to the next address in the subframe F_(j) (block 1040). Thedesubframer 220 can then determine whether i equals N (block 1042). If idoes not equal N, the desubframer 220 set i=i+1 (block 1044) and theflowchart can return to block 1036. If i does equal N, the frame (and/oran address in memory) can be sent to the decoder 222 (block 1046).

FIG. 11 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized for determining subframing strategies, similar tothe flowchart from FIG. 10. As illustrated in the nonlimiting example ofFIG. 11, the subframer 204 can receive frames from an encoder 202 (block1132). The subframer can then determine a subframing pattern (block1132). If a random pattern is determined, the subframer 204 can randomlyorder bits of the received frame into Dη complementary subframes (block1134).

If, at block 1132, a PCC pattern that might be used for a PCC code isdetermined, the subframer 204 can distribute the coded bits (systematic,parity, and interleaved parity bits) generated by the turbo (PCC) codeinto subframes (block 1136). First, the subframer 204 can distribute thecoded bits (systematic, parity, and interleaved parity bits) generatedby the same data bit into different subframes (if possible). Second, thedistribution may be completed such that all subframes contain the same(or close to the same) number of systematic bits. This second pointapplies similarly for parity and interleaved parity bits. Third, foreach coded sequence, the systematic bits allocated to the same subframemay be scattered in the original ordering. In other words, systematicbits that are contiguous in the original ordering may be distributed todifferent subframes (if possible. This third point applies similarly forparity and interleaved parity bits.

If, at block 1132, an LDPC pattern that might be used for an LDPC codeis determined, the subframer can divide the frame into Dη blocks of N/Dηbits that are contiguous in the frame. Each block may be a subframe.Similarly, the subframing pattern may be given by S(i)=ceil(i*Dη/N), fori an integer in {1, . . . , N} (block 1142).

FIG. 12 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframe interleaver, such as the subframeinterleaver from FIG. 2. As illustrated in the nonlimiting example ofFIG. 12, the subframe interleaver 206 can receive a symbol (D subframes)from the subframer 204 (block 1232). The subframe interleaver 206 canthen determine whether D=1 (block 1234). More specifically, D may bedetermined from an offline calibration. If D is equal to 1, theflowchart can proceed to block 1242, described below. If D is not equalto 1, the subframe interleaver 206 can determine an interleavingstrategy (block 1236). Again, in at least one nonlimiting example, thesubframe interleaving strategy may be determined from an offlinecalibration. If the first strategy is determined (described above), theflowchart may proceed to block 1240. If the second strategy isdetermined, the subframe interleaver can send a symbol (and/or anaddress associated with the symbol) to the symbol interleaver input(1^(st) device 324 a of FIG. 3A), as illustrated in block 1238. For J in{1, . . . D}, the subframe interleaver can send the j^(th) subframe(and/or an address associated with the subframe) forming a symbol to thej^(th) input of a periodic subframe interleaver (2^(nd) device 326 a ofFIG. 3A), as illustrated in block 1240. The subframe interleaver canthen send the symbol output to the mapper 210 (block 1242).

FIG. 13 is a flowchart illustrating an exemplary embodiment of a processthat may be utilized in a subframe deinterleaver, such as the subframedeinterleaver from FIG. 2. As illustrated in the nonlimiting example ofFIG. 13, the SPU 200 can receive a symbol (D subframes) from the eraser217 (block 1332). The subframe deinterleaver 324 b, 326 b can thendetermine whether D equals 1 (block 1334), where in at least oneembodiment, D is determined form an offline calibration. If D equals 1,the flowchart can proceed to block 1344. If D does not equal 1, for j in{1, . . . , D}, the j^(th) subframe (and/or an address associated withthe subframe) forming a symbol can be sent to the j^(th) input of theperiodic subframe deinterleaver 326 b (block 1336). The SPU 200 cangroup the D output subframes from the periodic subframe deinterleaver326 b into a symbol (block 1338). The interleaving strategy can bechecked (block 1340). As discussed above, the subframe interleavingstrategy may be determined from an offline calibration. If the firstsubframe interleaving strategy has been used on the transmitter, theflowchart proceeds to block 1344. If the second subframe interleavingstrategy has been used on the transmitter, the periodic subframedeinterleaver 326 b can send a symbol (and/or an address associated withthe symbol) to the input of the symbol deinterleaver 234 b (block 1342).The symbol deinterleaver 324 b can then send the symbol output (Dsubframes) to the desubframer, where η symbols may be received beforestarting the desubframing operation (block 1344).

The embodiments disclosed herein can be implemented in hardware,software, firmware, or a combination thereof. At least one embodimentdisclosed herein may be implemented in software and/or firmware that isstored in a memory and that is executed by a suitable instructionexecution system. If implemented in hardware, one or more of theembodiments disclosed herein can be implemented with any or acombination of the following technologies: a discrete logic circuit(s)having logic gates for implementing logic functions upon data signals,an application specific integrated circuit (ASIC) having appropriatecombinational logic gates, a programmable gate array(s) (PGA), a fieldprogrammable gate array (FPGA), etc.

One should note that the flowcharts included herein show thearchitecture, functionality, and operation of a possible implementationof software. In this regard, each block can be interpreted to representa module, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that in some alternativeimplementations, the functions noted in the blocks may occur out of theorder and/or not at all. For example, two blocks shown in succession mayin fact be executed substantially concurrently or the blocks maysometimes be executed in the reverse order, depending upon theoperations involved.

One should note that any of the programs listed herein, which caninclude an ordered listing of executable instructions for implementinglogical functions, can be embodied in any computer-readable medium foruse by or in connection with an instruction execution system, apparatus,or device, such as a computer-based system, processor-containing system,or other system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device. The computer readable medium can be, for examplebut not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device. More specificexamples (a nonexhaustive list) of the computer-readable medium couldinclude an electrical connection (electronic) having one or more wires,a portable computer diskette (magnetic), a random access memory (RAM)(electronic), a read-only memory (ROM) (electronic), an erasableprogrammable read-only memory (EPROM or Flash memory) (electronic), anoptical fiber (optical), and a portable compact disc read-only memory(CDROM) (optical). In addition, the scope of the certain embodiments ofthis disclosure can include embodying the operations described in logicembodied in hardware or software-configured mediums.

Additionally, embodiments discussed herein may be implemented in (and/orassociated with) one or more different devices. More specifically,depending on the particular configuration, operations discussed hereinmay be implemented in a set-top box, a satellite system, a television, aportable appliance, a gaming unit, a personal computer, an MP3 player,an iPod® player, a cellular telephone, a wireless communicationreceiver, a Digital Subscriber Line (DSL) modem, a wirelinecommunication system and/or other devices.

One should also note that conditional language, such as, among others,“can,” “could,” “might,” or “may,” unless specifically stated otherwise,or otherwise understood within the context as used, is generallyintended to convey that certain embodiments include, while otherembodiments do not include, certain features, elements and/or steps.Thus, such conditional language is not generally intended to imply thatfeatures, elements and/or steps are in any way required for one or moreparticular embodiments or that one or more particular embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements and/or steps are included orare to be performed in any particular embodiment. Additionally, use ofthe term “receive,” “receiving, “received,” and other similar terms isnot intended to limit the disclosure to actions taken at an input portand/or output port. Depending on the particular embodiment, the term“receive” (as well as variations thereof) may be interpreted to includeinternal and/or external communication of data.

It should be emphasized that the above-described embodiments are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of this disclosure. Many variations andmodifications may be made to the above-described embodiment(s) withoutdeparting substantially from the spirit and principles of thedisclosure. All such modifications and variations are intended to beincluded herein within the scope of this disclosure.

1. A self-protection unit for protecting a signal, comprising: a firstreceiving component configured to receive encoded data, the receiveddata being received as at least one frame; a subframing componentconfigured to subframe at least a portion of the received data, whereinsubframing includes converting the at least one into a plurality ofsubframes; and a subframe interleaver component configured to interleaveat least a portion of the subframes.
 2. The self-protection unit ofclaim 1, wherein the encoded data is generated by an encoder formed by aserial concatenation of an outer encoder device, an outer interleaverdevice, and an inner encoder device.
 3. The self-protection unit ofclaim 1, further comprising: a second receiving component configured toreceive demapped data; an error detector component configured to detectwhether a multicarrier symbol received from a channel has been corruptedby non-stationary noise; and an erasing component configured to erasedemapped data associated with at least one symbol that is corrupted bythe non-stationary noise.
 4. The self-protection unit of claim 1,further comprising a subframe deinterleaver component configured todeinterleave at least a portion of the subframes.
 5. The self-protectionunit of claim 1, further comprising a desubframer component configuredto desubframe at least a portion of the subframes.
 6. Theself-protection unit of claim 1, further comprising a calibrationcomponent configured to determine whether subframe interleaving isdesired; and a desired number of subframes per frame; a desiredinterleaving technique; and a desired subframing pattern.
 7. Theself-protection unit of claim 1, wherein the self-protection unit isembodied in at least one of the following: a set-top box, a television,a portable appliance, a gaming unit, a satellite system, an MP3 player,an iPod player, a cellular telephone, a wireline communications system,a Digital Subscriber Line (DSL) modem, and a wireless communicationsystem.
 8. A method for self protection, comprising: receiving data, thereceived encoded data being received as at least one frame; and dividingand reordering the at least one frame into a plurality of subframes, atleast one of the plurality frames being a subset of the at least oneframe.
 9. The method of claim 8, wherein the received data is receivedfrom an encoder formed by a serial concatenation of an outer encoderdevice, an outer interleaver device, and an inner encoder device. 10.The method of claim 8, wherein dividing and reordering the at least oneframe into a plurality of subframes includes determining a subframingpattern.
 11. The method of claim 8, wherein dividing and reordering theat least one frame into a plurality of subframes, includes randomlyordering the at least one frame into a plurality of subframes.
 12. Themethod of claim 8, wherein dividing and reordering the at least oneframe into a plurality of subframes, includes distributing systematic,parity, and interleaved parity bits generated by a turbo code into aplurality of subframes such that the systematic, parity, and interleavedparity bits generated by a common information bit are distributed todifferent subframes, wherein systematic bits generated by contiguousinformation bits are distributed to different subframes, wherein paritybits generated by contiguous information bits are distributed todifferent subframes, and wherein interleaved parity bits generated bycontiguous information bits are distributed to different subframes. 13.The method of claim 8, wherein each subframe includes elements that arecontiguous in the at least one frame.
 14. The method of claim 8, furthercomprising interleaving at least a portion of the subframes.
 15. Theself-protection unit of claim 5, further comprising at least a portionof the plurality of subframes.
 16. The method of claim 8, wherein atleast a portion of the method is performed in at least one of thefollowing: a set-top box, a television, a portable appliance, a gamingunit, a satellite system, an MP3 player, an iPod® player, a cellulartelephone, a wireline communications system, a Digital Subscriber Line(DSL) modem, and a wireless communications system.
 17. A system forprotecting a signal, comprising: means for receiving encoded data, thereceived data being received as at least one frame; means for subframingat least a portion of the received data, wherein subframing includesconverting the at least one into a plurality of subframes; and means forinterleaving at least a portion of the subframes.
 18. The system ofclaim 17, wherein the received data is received an encoder formed by aserial concatenation of an outer encoder device, an outer interleaverdevice, and an inner encoder device.
 19. The system of claim 17, furthercomprising: means for receiving demapped data; means for detectingwhether a multicarrier symbol received from a channel has been corruptedby non-stationary noise; and means for erasing demapped data associatedwith at least one symbol that is corrupted by the non-stationary noise.20. The system of claim 17, further comprising means for deinterleavingat least a portion of the subframes.
 21. The system of claim 1, furthercomprising means for desubframing at least a portion of the subframes.22. The system of claim 17, wherein the system includes at least one ofthe following: a set-top box, a television, a portable appliance, agaming unit, a satellite system, an MP3 player, an iPod® player, acellular telephone, a wireline communications device, a DigitalSubscriber Line (DSL) modem, and a wireless communication receiver.